1. Field of the Invention
The present invention relates to a three-dimensional input device for measuring the shape of an object by projecting a reference light on the object.
2. Description of the Related Art
Non-contact type three-dimensional input devices which are known as rangefinders are used for data input to computer graphics (CG) systems and computer-aided design (CAD) systems, physical (body) measurement, robot visual recognition and the like because these devices are capable of high speed measurement compared to contact-type devices.
The slit projection method (also referred to as "light-section method") is known to be suitable as a measurement method for rangefinders. This method optically scans an object to obtain a distance image (three-dimensional image), and is one type of dynamic measuring method for sensing an object by illumination with a specific reference light. The distance image is a collection of pixels expressing a three-dimensional position at a plurality of parts of an object. In the slit projection method, a slit light having a linear band-like projection beam cross section is used as a reference light.
A two-dimensional color photography function is used in the rangefinder. A photographed two-dimensional image is displayed on a monitor via an internal or external display device, and a user uses the reference information when determining the field angle of the three-dimensional measurement. Two-dimensional photography is accomplished at the same field angle as three-dimensional measurement, and the obtained two-dimensional image is combined with the three-dimensional data and either output or stored as the measurement result. When viewing the two-dimensional image, a user can readily confirm the measured object, and the two-dimensional image may be used for correction or processing of the three-dimensional data.
In a conventional rangefinder, an aperture is not provided in the light-receiving optical path so as to allow as much reference light reflected by an object as possible to enter the photoreceptive surface of the photoelectric converter. Two-dimensional photography is accomplished by automatic exposure control via an electronic shutter, and three-dimensional measurement is accomplished by optimizing the amount of light entering the photoreceptive surface by adjusting the projection intensity of the reference light. A disadvantage of this construction is that in two-dimensional photography the depth of the field cannot be increased, and the aberration produced by the lens cannot be ignored. This disadvantageously produces a small S/N ratio. In three-dimensional measurement, when the projection intensity is reduced, the effect of the background light increases so as to reduce the measurement accuracy.